Multiple disc brake system

ABSTRACT

A disc brake system comprising a disc, and a hub which is arranged to rotate about an axis thereof. The system also comprises a mounting arrangement by which the disc is mounted on the hub so that the hub and the disc rotate as a unit about the axis and the disc can perform axial sliding movement on the hub. The system also comprises a plurality of leaf springs mounted on the hub and engaging the disc so that the springs apply radially-directed forces between the disc and the hub. Each of the springs comprises at least three abutments which project transversely of the spring and engage the disc so that the abutments apply forces to the disc.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention is concerned with a disc brake system, for example for awheel of a vehicle.

2. Related Art

A conventional disc brake system comprises a hub mounted on a suspensionlink for rotation relative thereto, the hub providing a mounting for awheel, and a disc brake comprising a brake disc mounted for rotationwith the hub, friction material pads arranged on opposite sides of thedisc, and at least one piston and cylinder assembly operable to urge thepads into engagement with the disc, to brake the hub and hence thewheel. Conventionally, the piston and cylinder assembly is slidablymounted on a slide bolted to the suspension link of the vehicle. Thedisc is conventionally rigidly fixed to the hub, and wear of the padsand/or the disc is accommodated by the sliding movement of the cylinder.

Disc brake systems are known in which the disc rotates with the hub as aunit but can perform sliding movement on the hub. For example, see GB 1396 503. However, such systems are associated with technical problems.For example, since the discs are relatively thin, they tend to tilt onthe hub and affect the braking ability. Also, there is a tendency fornoise to be produced by rattle of the disc against the hub. At higherdisc temperatures, these problems can be particularly severe since, whenthere is a large temperature differential, such as 600° C., between thebraking surface of the disc and the hub, the disc expands considerably,away from the hub, exacerbating the problems of tilting and rattle.These problems are addressed in WO 98/26192 in which the solutionproposed is to provide a plurality of resilient force applicators whichare mounted between the hub and the disc, the force applicators actingto apply radially-directed forces to the disc to control the movementthereof, the force applicators being distributed circumferentiallyaround the hub. In one of the embodiments proposed in WO 98/26192, theforce applicators are leaf springs and each leaf spring may be securedto the outer surface of the hub in a manner such that the spring extendstangentially of the hub when the disc is not mounted on the hub. Thespring is resiliently deformed when the disc is mounted on the hub. Thecentral portion of each leaf presses against the hub while the extremeends thereof press against the disc. Thus, in the case of 3 leaf springsas shown in FIG. 1 of WO 98/26192, the disc is engaged at 6 points bythe springs. DE 2039003 A discloses use of springs to applyradially-directed forces between a slidable disc and its hub, thesprings being shaped leaf springs with their centres bearing on one ofthe hub or the disc and their ends bearing on the other.

It is an object of the present invention to improve the control of themovement of a disc on a hub provided by leaf springs similar to thosedisclosed in WO 98/26192.

SUMMARY OF THE INVENTION

The invention provides a disc brake system comprising a disc, and a hubwhich is arranged to rotate about an axis thereof, the system alsocomprising mounting means by which the disc is mounted on the hub sothat the hub and the disc rotate as a unit about said axis and the disccan perform axial sliding movement on said hub, the system alsocomprising a plurality of leaf springs mounted on the hub and engagingthe disc so that the springs apply radially-directed forces between thedisc and the hub, characterised in that each of said springs comprisesat least three abutments which project transversely of the spring andengage the disc so that the abutments apply forces to the disc.

In a disc brake system according to the invention, the abutments eachprovide a point of contact with the disc so that the number of points ofcontact between the disc and each spring is increased, in comparisonwith the system disclosed in WO 98/26192. This reduces the force actingat each such point of contact. This gives improved control of the discmovement.

A disc brake system according to the invention may be of the typedisclosed in WO 98/25804. That brake system comprises two discs whichare slidable on the same hub under the control of leaf springs which actbetween the hub and the discs. The system also comprises a cylinderwhich is integrally formed with a suspension link and a caliper alsofixed to the suspension link, the caliper having supports for frictionpads mounted thereon. In such a system, leaf springs as disclosed hereinreplace the leaf springs disclosed in WO 98/25804 which act between thehub and the discs.

In a disc brake system according to the invention, said abutments may beprovided by embossed portions of the spring. Such embossments may have agenerally semi-cylindrical form. Alternatively, the abutments may beprovided by material deposited on the spring and secured thereto.

Said abutments may be elongated so that each abutment remains inengagement with the disc throughout said movement of the disc on thehub.

Said abutments may be in the form of ridges extending parallel to theaxis about which the hub rotates.

The leaf springs of a disc brake system according to the invention maybe secured to the outer surface of the hub in a manner such that thesprings extend tangentially of the hub when the disc is not mounted onthe hub.

In a disc brake system according to the invention, cut-outs may beformed in the leaf springs to control the force applied by the abutmentsto the disc. Such cut-outs may be in the form of holes through thespring or may be cut into the edges of the spring.

A disc brake system according to the invention may comprise one or morefurther discs mounted on the hub. In this case, each leaf spring mayhave abutments which engage all of the discs. Alternatively, the leafsprings may be arranged in groups, one spring in each group beingassociated with each disc, at least one spring in each group beingretained in position by a connection to another spring in said group.

Said mounting means of the disc on the hub may compriseaxially-extending grooves formed in an external surface of said hub andteeth projecting from said disc into said grooves, the teeth being asliding fit in said grooves. In this case, said leaf springs may belocated within said grooves and engage said teeth.

There now follows a detailed description, to be read with reference tothe accompanying drawings, of a disc brake system which is illustrativeof the invention.

THE DRAWINGS

In the drawings:

FIG. 1 is an end view of the illustrative disc brake system;

FIG. 2 is a cross-sectional view, on a larger scale, taken on the brokenline II—II in FIG. 1;

FIG. 3 is a perspective view, on a greatly enlarged scale, of a leafspring of the illustrative disc brake system;

FIG. 4 is a view similar to FIG. 3 but of an alternative leaf spring ofthe illustrative disc brake system; and

FIG. 5 is a perspective view like FIG. 3, but embodying an alternativeleaf spring mounting system.

DETAILED DESCRIPTION

The illustrative disc brake system 10 shown in FIGS. 1 and 2 is for awheel (not shown) of a car. The system 10 comprises a disc 12, a furtherdisc 14 and a hub 16, on which the wheel can be mounted. The hub 16 isarranged to rotate about a central axis 18 thereof.

The hub 16 comprises an internally splined hollow inner cylindricalportion 16 a which is arranged to receive a drive shaft (not shown)which drives the wheel. The hub 16 also comprises an external flange 16b at one end of the portion 16 a. This flange 16 b has four bolt holes16 c through which the wheel can be bolted to the flange 16 b in aconventional manner. The flange 16 b also serves to connect the portion16 a to an outer hollow cylindrical portion 16 d of the hub 16.

The discs 12 and 14 are identical to one another, being in the form ofgenerally-annular cast iron or steel plates. The two discs 12 and 14 aremounted by means of mounting means of the system 10 on the cylindricalouter surface of the hub portion 16 d so that the hub 16 and the twodiscs 12 and 14 rotate as a unit about the axis 18 and the discs 12 and14 can perform axial sliding movement on said hub 16. The mounting meanscomprises four grooves 20 which are formed in the outer cylindricalsurface of the portion 16 d of the hub 16 and four teeth 22 whichproject inwardly from each of the discs 12 and 14. The teeth 22 enterthe grooves 20 and are a sliding fit therein. However, the teeth 22 donot extend to the bottom surfaces 20 a of the grooves 20, there being aclearance between the bottom surfaces 20 a and the inner surfaces 22 aof the teeth 22. The grooves 20 are equally-spaced circumferentiallyabout the axis 18 and each occupies an arc of approximately 45° aboutthe axis 18. Between the grooves 20, the outer surface of the hubportion 16 d is machined to be accurately cylindrical about the axis 18.The inner surface of each disc 12 and 14, between the teeth. 22, is alsomachined to be accurately cylindrical about the axis 18 and a close fitover the cylindrical portions of the outer surface of the hub portion 16d. The close fit of the discs 12 and 14 on the hub 16 reduces thepossibility of the discs 12 and 14 tipping.

The system 10 also comprises four friction pads 26 (FIG. 2) for brakingthe discs 12 and 14 by engaging side surfaces of the discs. The frictionpads 26 are secured to three backing plates 28, one backing plate 28 abeing between the discs 12 and 14 and the others being on opposite sidesof the discs 12 and 14 to the plate 28 a. The median plate 28 a hasfriction pads 26 secured to both of its faces. The brake pads 26 and thebacking plates 28 are not shown in FIG. 1. The friction pads 26 arebrought into braking contact with the discs 12 and 14 by operating means(not shown) which may be similar to that described in WO 98/25804. Whenthe operating means is operated, it moves one of the outer frictionmaterial pads 26 towards the other outer pad 26 which isfixedly-mounted. This causes movement of the pads 26 and discs 12 and 14until the each disc 12 and 14 is engaged on both sides by a pad 26. Thediscs 12 and 14 slide axially on the hub 16 and the plate 28 a slidesaxially on a slideway to accommodate this movement.

The system 10 also comprises four leaf springs 32 mounted on the hub 16and engaging the discs 12 and 14 so that the springs 32 applyradially-directed forces between each of the discs 12 and 14 and the hub16 to control movement of the discs on the hub. The leaf springs 32 areequally distributed circumferentially around the hub 16, each beingmounted on one of the bottom surfaces 20 a of the grooves 20, ie thesprings 32 are mounted in the grooves 20 and act between the surface 20a and the inner surface 22 a of the tooth 22 which enters the groove 20.

One of the leaf springs 32 is shown in detail in FIG. 3. Each spring 32is formed from a generally rectangular piece of spring steel which is0.25-0.3 mm thick. Each spring 32 is secured in the circumferentialcentre of one of the surfaces 20 a by means of a central screw 36 whichpasses through a hole 32 a in the spring 32 and enters the hub 16. Eachspring 32 extends axially on the hub 16 throughout the range of axialmovement of both discs 12 and 14 so that both discs 12 and 14 areengaged by all four of the springs 32 continuously. The springs 32 actto control the sliding movement of the discs 12 and 14 on the hub 16preventing tipping of the discs and compensating for thermal expansioneffects.

Each spring 32 comprises four axially-extending abutments 40 whichproject transversely of the spring 32. The abutments 40 are arrangedwith two of the abutments on each side of the hole 32 a. Two of theabutments 40 are formed at the extreme ends of the spring 32, therebypreventing the edge of the spring 32 from engaging the tooth 22 andreducing the risk of cracking of the spring 32. Between the twoabutments 40 on each side of the hole 32 a, a rectangular hole 32 b iscut out of the spring 32. The hole 32 b serves to control the forceapplied by the abutments 40 to the discs 12 and 14.

The abutments 40 are provided by embossed portions of the spring 32which are in the form of generally semi-circular (in transversecross-section) ridges extending parallel to the axis 18. The abutments40 are elongated in the axial direction so that each abutment 40 remainsin engagement with both of the discs 12 and 14 throughout the movementof the discs 12 and 14 on the hub 16.

Each spring 32 is arranged to engage the discs 12 and 14 with itsabutments 40 and apply forces to the discs to control the movementthereof on the hub 16. Each spring 32 is arranged so that the spring 32extends generally tangentially of the hub 16 when the discs 12 and 14are not mounted on the hub 16. However, the springs 32 are deformed bythe presence of the discs 12 and 14 so that each abutment 40 pressesresiliently on the discs 12 and 14. The springs 32, thus, act to applyradially-directed forces to the discs 12 and 14.

In the operation of the disc brake system 10, the springs 32 asaforementioned control the sliding movement of the discs 12 and 14 onthe hub 16. Each spring 32 engages each disc at four points of contact,provided by the abutments 40, thereby distributing the forces applied bythe spring 32 to each disc more uniformly.

FIG. 4 shows two leaf springs 42 which are joined together by a narrowtab 44, the springs 42 and the tab 44 being formed from a single sheetof spring steel. The two leaf springs 42 each have a similar form to thespring 32 except that the holes 32 b are omitted, each spring 42 havingfour abutments 46 which are similar to the abutments 40 of the spring32. However, the springs 42 are narrower than the spring 32 because eachspring 42 is intended to engage only one of the discs 12 and 14. Thesprings 42 are mounted on the surfaces 20 a as a unit connected by thetab 44 by means of a screw (not shown) which passes through a hole 42 aformed in one of the springs 42. Thus, each of the discs 12 and 14 hasfour of the leaf springs 42 associated therewith, the springs 42 beingarranged in groups of two, one of which is mounted on the hub and theother of which is retained in position by the connection, via the tab44, to the first-mentioned spring. As the tab 44 is narrow, the springs42 act substantially independently.

In modifications of the springs 32 and 42, the holes 32 a and 42 a maybe omitted and the springs provided instead with self-retaining meansfor retaining them on the hub 16. For example, such self-retaining meansmay comprise integral tabs 45 extending from the spring over oppositeends of the hub 16 so that the springs can be clipped over the hub. Inthe case of the spring 32, such tabs extend normally to the generalplane of the spring from both the edges of the spring which areperpendicular to the projections 40. In the case of the springs 42, eachof the end springs 42 in a group has one of these tabs extending fromits opposite edge to the position of the tab 44.

In a further modification, the springs 32 and 42 can be formed into anon-planar form in order to determine the forces they will apply to thedisc. For example, the springs can be formed into an arcuate shape suchthat, when the spring is mounted on the hub but before the discs aremounted on the hub, the ends of the spring are further from the hub thanif the spring were planar.

What is claimed is:
 1. A disc brake system comprising a disc, and a hubwhich is arranged to rotate about an axis thereof, the system alsocomprising mounting structure by which the disc is mounted on the hub sothat the hub and the disc rotate as a unit about said axis and the disccan perform axial sliding movement on said hub, the system alsocomprising a plurality of leaf springs mounted on the hub and engagingthe disc so that the springs apply radially-directed forces between thedisc and the hub, wherein each of said springs comprises at least threeabutments which project transversely of each of said springs and engagethe disc so that the abutments apply forces to the disc.
 2. A disc brakesystem according to claim 1, wherein said abutments are provided byembossed portions of each of said springs.
 3. A disc brake systemaccording to claim 1, wherein said abutments are elongated so that eachabutment remains in engagement with the disc throughout said movement ofthe disc on the hub.
 4. A disc brake system according to claim 1,wherein said abutments are in the form of ridges extending parallel tothe axis about which the hub rotates.
 5. A disc brake system accordingto claim 1, wherein the leaf springs are secured to the outer surface ofthe hub in a manner such that the springs extend tangentially of the hubwhen the disc is not mounted on the hub.
 6. A disc brake systemaccording to claim 1, wherein cut-outs are formed in the leaf springs tocontrol the force applied by the abutments to the disc.
 7. A disc brakesystem according to claim 1, wherein the system comprises one or morefurther discs mounted on the hub, and in that the leaf springs arearranged in groups with each group comprising two springs, said twosprings constructed as a single piece and being joined to one another bya tab, one spring in each group being associated with one disc, at leastone spring in each group being retained in position by being joined bysaid tab to the other of the springs in said group.
 8. A disc brakesystem according to claim 1, wherein said mounting structure of the discon the hub comprises axially-extending grooves formed in an externalsurface of said hub and teeth projecting from said disc into saidgrooves, the teeth being a sliding fit in said grooves, and in that saidleaf springs are located within said grooves and engage said teeth.
 9. Adisc brake system according to claim 1, wherein the leaf springs are